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In the Wood River Valley, water flows from the high country into creeks and down into underground reservoirs, or aquifers, before bubbling out in portions of the Bellevue Triangle. For many years, that water has been diverted into irrigation ditches for agricultural use.

In more recent years, water has been pumped from wells for use in homes and for watering lawns and parks. How much water is used by whom has become an important question as the value of water rights increases and annual flows decrease.

A three-year-long publicly funded project to model groundwater flows in the Wood River Valley was launched Tuesday by the Idaho Department of Water Resources and the U.S. Geological Survey. The model will use data gathered from well-drilling logs, in-stream water gauges, geophysical testing and other sources.

The groundwater flow model will be constructed to simulate the effects of human use and climate change on the aquifer system. It could also be the first step toward administering groundwater rights along with surface water rights, a practice known as “conjunctive management.”

“The model will be designed to be used in conjunctive management [of water resources],” said Sean Vincent, hydrology section manager of the Idaho Department of Water Resources.

Under conjunctive administration, senior water rights holders, such as the Big Wood Canal Co. in southern Idaho, could potentially limit groundwater consumption for irrigation upstream in places such as Hailey, which has subordinate water rights.

Vincent and U.S. Geological Survey project manager Jim Bartolino spoke Tuesday to an audience of about 40 people at Wood River High School. Included were public officials, hydrologists, attorneys and water managers.

Vincent said the groundwater flow model will provide insight into the cause of water flow declines, including declines due to consumptive uses.

“Evapotranspiration (the combined loss of water to evaporation and plant transpiration) is what you look at the end of the day,” he said.

The scientists showed a report of data already gathered from the Big Wood River during the past 90 years. The report included the following findings:

A mean monthly increase in flows at the Croy Canyon measuring station during March, “possibly because of earlier snowpack runoff.”

A mean annual decrease since the 1940s of about 15 cubic feet per second at a stream gauging station near Bellevue. The mean monthly water discharge at this point during winter months also showed “decreasing trends,” which results in less water for irrigators downstream.

A third point of measurement, at the Silver Creek sportsmen’s access near Picabo, showed decreases in annual discharge during the period 1975 to 2005.

“Because Silver Creek and its tributaries are fed primarily by groundwater through seeps and springs, seasonal fluctuations in groundwater levels affect streamflow,” the report said.

The basic groundwater flow model presented Tuesday showed that well pumping out of the aquifer in the upper Wood River Valley could affect groundwater flows at Silver Creek.

The model could also show that well pumping since a residential development boom began in the 1970s in the Wood River Valley has depleted river flows and downstream irrigation water resources. Concern has risen within the city of Hailey that the model could be used to support claims by canal companies to the south that northern users have to cut back on water use during dry years, especially for watering lawns and parks, which is considered a “consumptive use,” and subject to curtailment.

Hailey Mayor Fritz Haemmerle, a water rights attorney, called for a review of the city’s water rights portfolio in advance of the Tuesday presentation on the groundwater flow model project, saying the project poses a “significant threat” to well users in Hailey.

Haemmerle said the city would also research mitigation plans to use in case of a “call” upon the city’s water from downstream.

“Quite possibly, water rates in the city will be going up” as a result of the new studies, he said.

Vincent and Bartolino asked for volunteers to join a Modeling Technical Advisory Committee, which will provide input on modeling techniques and provide additional measurement data over the next three years. Bartolino will serve the project as lead investigator.

“We want no lobbyists and no attorneys on the committee,” Vincent said, indicating the highly politicized nature of water rights allocation in the region.

The first meeting of the Modeling Techincal Advisory Committee will take place on April 11 at 6:30 p.m. in Room 200 at the Community Campus in Hailey.